I hadn't used one in a while (a ww), however, my last hatch I just used a cheap digital medical thermometer, that I got for my kids. I just had to push the button vs it being on all the time, but I was very happy with the accuracy.
I use a water wiggler with my Brinsea Spot Checks; Spot Checks range from $22-30 apiece and the wigglers are $1 if you can find them at Dollar Tree. They're usually where the little kids' toys are at.
I didn't use a water wiggler. I couldn't find one so I made my bator without it. My temps seem to be fine and so far all the eggs appear to be fertile and doing good.
I hope they all hatch.